whether you have to delete the dima or not depends on the character of the planning scenario, e.g.

a busines2customer parcel delivery usually deletes the distance matrix each day (or with each call) because he visits OTHER locations each day.

a business2business parcel delivery could recycle a distance matrix because the locations do not change (maybe just some new customers)

Maybe we can give some more detailed info if we know more about your scenario.

In times of high performance routing you can also try to delete and recreate the DIMA with each new order scenario because the calculation from scratch is quite fast.

If you want to play with a specific order scenario (e.g. dispatcher manipulates tours manually or changes some parameters like operating intervals...) then you can recycle the DIMA as long as the dispatcher is in the same planning "topic".